Relation of Sleep-Entrained Human Prolactin Release to REM-NonREM Cycles

Human plasma prolactin (hPRL) concentrations were measured by radioimmunoassay in samples drawn at 20-min intervals from 14 normal male subjects during 58 nights of polygraphically monitored sleep. The hPRL-sleep histogram plots often showed a cyclic relation between recurrent REM periods and hPRL nadirs and between subsequent nonREM (Stage 2–4) segments and hPRL rises and peaks. The hPRL data were then tabulated as REM, nonREM or Wake values. To allow comparison between subjects and between sleep cycles of different lengths, sleep onset and the ends of REM periods were used as reference points within each sleep pattern. Backward from these reference points at 20-min intervals were tabulated pre-sleep Wake and REM values, respectively. Forward from these points, at 20-min intervals, were tabulated nonREM values. Thus, these tabular hPRL data now represented release patterns within sequential sleep onset and REM–nonREM cycles across sleep. Subject and group averages of these data clearly evidenced a temporal relation between REM–nonREM cycles in sleep and the respective progression in hPRL nadirs and peaks across sleep, in which cyclic hPRL nadirs in REM were significantly less than subsequent hPRL peaks in nonREM segments of these sequential sleep cycles. Entrainment of episodic hPRL release to sleep and more specifically to REM–nonREM cycles within sleep was indicated by these data. Hypothalamic dopaminergic correlates of Stage REM resulting in PIF release may explain these hPRL nadirs in part, though descent from nonREM peak prior to occurrence of the next REM period indicated this was not the sole explanation. A more complex sequential relationship in sleep perhaps finally involving serial PIF-PRF release is suggested.